The formwork failure occurred on an elevated section of the project to build the final length of the A7 motorway between Malaga and Almaria on the southern coast of Spain.
The Public Works Ministry commissioned the new section of road that runs through the Granada province.
A consortium of three Spanish companies won the .157M (£105M) contract to build the 9.12km section of road through the mountainous terrain.
The new stretch includes four viaducts, of which the one near Almuñécar was one. There are also five overpasses, three underpasses and three tunnels.
The Spanish consortium, Azvi, Ploder and Obras Subterraneas, subcontracted the deck work on the viaduct to Puentes y Calzadas. It subcontracted the labour to the Portuguese company Douro.
Work began in September 2002 and is expected to be completed by October 2007.